Gaseous restraint of conveyed articles



y 1963 M. D. JEPSON 3,096,162

GASEOUS RESTRAINT OF CONVEYED ARTICLES Filed Feb. 18, 1959 5Sheets-Sheet l Inventor Attorneys uly 2, 1963 M. D. JEPSON 3,096,162

GASEOUS RESTRAINT 0F CONVEYED ARTICLES Filed Feb. 18, 1959 3Sheets-Sheet 2 144 R/AJL E SPEED -FIG. 2.-

Inventor W kw By W Attorn ys y 1963 M. D. JEPSON 3,096,162

GASEOUS RESTRAINT OF CONVEYED ARTICLES Filed Feb. 18, 1959 3 SheetsSheet3 R z: :9, Q- I/ "i LMJ LJ Inventor A Horn e y-s United States Patent3,996,162 GASEGUS RESTRAHQT GF CONVEYED AR'llfiLES Michael Denis Jepson,llkley, England, assignor to The Spooner Dryer & Engineering Co.Limited, Ehley, England Filed Feb. 18, 1959, Ser. No. 794,005 Claimspriority, application Great Britain Feb. 19, 1953 2 Claims. (1. 34-33)The present invention relates to a method of and apparatus for thermallytreating in succession a plurality of discrete light-weight articlessuch as moulded pulp articles.

It is well known to thermally treat materials for purposes such asdrying by transferring heat thereto by convection by directing aplurality of streams of heated gaseous medium towards the material so asto impinge thereon at high velocity whilst the material is moved along agiven path.

Such a process is eminently suitable for the thermal treatment ofsubstantially continuous strip or web material such as, for example,textiles, but practical diniculties arise in the application of such aprocess to light weight articles such as moulded pulp articles, in thatthe articles are often displaced from their given path by theimpingement of the high velocity streams.

The present invention envisages providing a perforate conveyor forlight-weight articles to be subjected to thermal treatment andestablishing a pressure drop across the conveyor so as to resistdisplacement of the articles when subjected to the impingement of highvelocity streams of gaseous medium.

Thus, according to one feature of the present invention a method ofthermally treating discrete light-weight articles, such as moulded pulparticles, on a perforate conveyor, comprises directing a plurality ofstreams of heated gaseous medium towards articles on the conveyor so asto impinge the articles at high velocity, and establishing a pressuredrop across the conveyor with the pressure at the side of the conveyorremote from the articles thereon lower than the pressure at thearticleside of the conveyor.

In the method of the present invention when applied to the drying ofmoulded pulp articles the drying is effected by evaporation due to theimpingement of the high velocity streams. There is comparatively littleor no removal of water in liquid phase by the suction effected by thepressure drop across the conveyor. Care should be taken that thepressure drop across the conveyor is suiiicient to retain the articlesin place on the conveyor but is not excessive. Excessive suction maycause the articles, particularly paper pulp articles, which are veryweak in their wet state, to become distorted and may even cause thearticles to be flattened on to the conveyor.

In order that gaseous medium may be directed on to said articles at asubstantial rate, and yet only a small pressure drop be maintainedacross the conveyor, it is necessary for some of the gaseous medium sodirected to be withdrawn from the same side of the conveyor as articlesthereon.

Thus, according to another feature of the present invention, a method ofthermally treating discrete lightweight articles, such as moulded pulparticles, on a perforate conveyor, comprises directing a plurality ofstreams of gaseous medium towards articles on the conveyor so as toimpinge the articles at high velocity, withdrawing at the article-sideof said conveyor gaseous medium so directed and circulating saidwithdrawn gaseous medium in an endless path of which a portion isoccupied by said streams, imparting heat to said gaseous medium beforeEfidfidd? Fatented .luly 2, 1963 directing it towards said articles, andwithdrawing gaseous medium from a zone at the side of said conveyor'remote from said articles to establish a pressure drop across saidconveyor.

The invention includes apparatus for thermally treating a plurality ofdiscrete articles, said apparatus comprising a perforatearticle-receiving conveyor for conveying articles along a given path, atleast one pressure chamber spaced from said conveyor with said givenpath therebetween and having a plurality of nozzles for the discharge ofstreams of heated gaseous medium at high velocity towards said conveyorand articles thereon, at least one suction chamber disposed with an openface thereof adjacent said conveyor at least in the region of saidpressure chamber and on the opposite side of said conveyor to said givenpath, means including said pressure chamber and said nozzles, butexcluding said suction chamber, defining a substantially enclosedendless path, means for circulating gaseous medium along the saidendless path, means for imparting heat to said gaseous medium socirculated, and means for withdrawing gaseous medium from said suctionchamber to establish a pressure drop across the perforate conveyor.

The pressure chamber, and part of the suction chamber may be disposedwithin an outer casing through which the conveyor passes said casing inpart defining said endless path. The suction chamber preferably extendsoutside the casing in the regions of entry and exit of articles on theconveyor so that articles can be subjected to the pressure drop acrossthe conveyor before they are subjected to the streams or jets. Gaseousmedium withdrawn from the suction chamber can also be mixed with thegaseous medium circulated in said endless path. The gaseous medium canbe circulated by a circulating fan and the gaseous medium can bewithdrawn from the suction chamber either by the same fan or by aseparate suction fan. It the same fan is used both to withdraw gaseousmedium from the suction chamber and to recirculate some of the gaseousmedium after discharge from the nozzles, means for throttling the flowof the gaseous medium withdrawn after discharge by the nozzles will benecessary in order to establish a pressure drop across the perforatedconveyor. If a separate suction fan is used for extracting gaseousmedium from the suction chamber the gaseous medium so withdrawn can beadded to the gaseous medium circulated in said endless path eitherupstream or downstream of the circulating fan. The means for heating thegaseous medium circulated in the endless path may be in the form of aheat exchanger to which a hot fluid such as steam may be supplied froman external source or may be an electric heater or may comprise a burnerfor the combustion of fuel the products of combustion therefrom beingadded to and intermingled with the gaseous medium circulated in theendless path to impart heat thereto. If the heater is in the form of aburner it is preferable for the fan withdrawing the gaseous medium fromthe suction chamber to discharge into the endless path upstream of thelocation of the burner which may be conveniently sit uated near theinlet of the circulating fan, since in this way the temperature of thegaseous medium passing through the circulating fan for given operatingconditions can be less than would arise if the gaseous medium withdrawnfrom the suction chamber were discharged downstream of the circulatingfan.

The conveyor may conveniently be in the form of flat surfaced perforatedmetal sheeting connected at its ends to a pair of sprocket chainsrunning on chain guides through the apparatus. The degree of perforationof the perforated sheet may conveniently be in the range of 20 to 40% ofthe surface area.

It is found in practice that satisfactory operation can be achieved withonly a slight pressure drop across the perforated conveyor, for examplea pressure drop of up to 1 inch water gauge (at 60 F.) will enable alarge range of articles to be retained on the conveyor andsatisfactorily to withstand the impingement of the high velocity jets ofgaseous medium Without becoming thereby displaced to any marked degreerelatively to the conveyor. Satisfactory operation has been achieved,for example, when a static pressure of approximately 2 inches watergauge (at 60 F.) obtains in the pressure chamber and a pressure drop ofabout a 4 inch water gauge across the conveyor and with the staticpressure in the region of the article receiving surface of the conveyoreffectively equal to atmospheric pressure. Such conditions are suitablefor the drying of light weight moulded pulp articles weighing forexample less than 36 gms. each, using air as circulated gaseous medium.

The invention will be further described by way of example with referenceto the accompanying diagrammatic drawings in which:

FIG. 1 is a longitudinal elevation of one form of apparatus according tothe present invention and with one side removed for the purpose ofillustration,

FIG. 2 is a transverse section along the line IIII of FIG. 1, and

FIG. 3 is a detail longitudinal elevation of a modification.

The apparatus illustrated in the drawings comprises a main framework andcasing through which there extends one pass of a perforated conveyor 11for receiving articles 12 to be treated. Disposed above the path of theconveyor 11 are one or more pressure chambers 13 having along theirlowersurfaces a plurality of downwardly directed nozzles 14.

The embodiment illustrated in the drawings is a two stage apparatushaving two such pressure chambers but it will be understood that theinvention is not limited as to the number of pressure chambers and mayinclude any number of stages according to the treatment required.

Each pressure chamber '13 has associated therewith a fan 15 driven by anelectric motor 16 and is connected by ducts .17, 1h to the outlet ofsuch fan. Inlet 19' of the fan 15 communicates with the interior of thecasing 10 so that air discharged by the fan 15 passes through the ducts.17, 18 into the pressure chamber 13 whence it is discharged throughnozzles 14 towards the conveyor and articles thereon, the path of suchbeing illustrated diagrammatically by the arrows 20. Air can then bewithdrawn from between the pressure chamber 13 and the conveyor 11 asillustrated by the arrows 2 1 and pass to the inlet 19- of the fan 15which can thus circulate at least part of the air along an endless path.For heating the circulated air there is disposed adjacent the inlet 19of the 'fan 15 a burner indicated diagrammatically at 22 in which fuelis combusted so that the products of combustion therefrom are introducedinto and mingle with the circulated gaseous medium which is heatedthereby.

Disposed beneath the path of the conveyor v11 in the region of eachpressure chamber :13 is a suction chamber 23 in the form of an opentopped chamber upon which rests a perforated article-receiving portion24 of the conveyor 11. The suction chamber 223 communicates through aconduit 25 With the inlet of a suction fan 26 having an outlet whichcommunicates through a duct 27 with the interior of the apparatus casing10.

Withdrawal of air from the suction chamber 23 as illustrated by arrows43 establishes a pressure drop across the perforated article-receivingportion 24 of the conveyor.

The conveyor '11 comprises a pair of sprocket chains 28, 29, running onguide rails 30, 31 and driven in any suitable manner (not shown). Thearticle-receiving portion 24 of the conveyor is in the form of aperforated metal sheeting. In practice it is found that satisfactory 4results can be obtained if the extent of the perforations amount toapproximately 20 to 40% of the surface area. Part of the or 'a suctionchamber 2?: extends outside the casing 10 in the region of entry ofarticles as at 32 andin the region of exit of articles as at 33.

In operation the conveyor 11 is set in motion with its upper pass movinginthe direction indicated by the arrows 34, the fans 15, 26 operate andfuel is ignited at the burners 22. Articles to be treated are placed insuccession upon the conveyor and thereon conveyed through the apparatus.When the pass of the conveyor 11 on which the articles are receivedcomes over the suction chamber part '32 the articles are subjected tothe pressure drop across the conveyor and can thereby be retained on theconveyor. When the articles come beneath the pressure chambers 13 theyare subjected to the impingement of high velocity jets or streams ofheated air from the nozzles 14, and on their undersides, through theperforations in the article receiving portion 24, they continue to besubjected to the reduced pressure existing in the suction chambers 23which serves to enable the articles to be retained on the conveyorwithout becoming disturbed or displaced to any marked extent byimpingement of the high velocity stream. The apparatus of the presentinvention is eminently suitable for the treatment of moulded pulparticles such as food trays and which are'light in weight; for examplemoulded pulp food trays Weighing in the region of 5 to 30 grammes can betreated when the fans .15 and 26 are operated to produce a staticpressure of about 2. inches Water gauge (at 60 F.) in the pressurechamber 13 and a vacuum of about /4 inch water gauge in the suctionchambers 23, with the static pressure inside the casing it adjacent thesides of the conveyor 11 eifectively equal to atmospheric pressure.

For the thermal treatment of moulded pulp articles it is preferable forthe conveyor 11 to have a substantially flat surface thereby enablingsuch articles to be dried without any substantial buckling. However, theconveyor 11 may alternatively have a wire mesh articlesupportiug portion24-.

In the embodiment shown a separate suction chamber 23 is providedbeneath each of the pressure chambers v13 but it will be understood thata single suction chamber may extend beneath more than one pressurechamber. If more than one suction chamber is provided each maycommunicate with a suction fan 26 individual thereto or alternativelyany number of suction chambers can communicate with such a fan which mayreturn air withdrawn from the suction chambers into the casing at morethan one point.

The embodiment illustrated in FIGS. 1 and 2 is a single pass apparatusin that articles are received at one end and are discharged at theother. It it should be desired that articles should be received anddischarged at the same end of the apparatus the suction chamber orchambers 23 can also be open bottomed and the lower pass 35 of theconveyor 11 can lie thereagainst as illustrated in FIG. 3 so thatarticles after passing through the apparatus along the upper pass 36 ofthe conveyor can be guided thereon around conveyor turning device 37 andcarried back beneath the lower pass 35 on which they are retained by theaction of the reduced pressure in the suction chamber 23. Articles canbe retained on the conveyor from one pass to the other by extending thesuction chamber 23 as at 38 so that a pressure drop exists across theconveyor from where it emerges from the casing at 39, around the turningdevice 37 and until and beyond where it re-enters the casing at 40.Alternatively a continuous moving felt may be arranged adjacent theconveyor 1'1 from near its point of emergence 39' to near its point ofre-en-try 46 to sandwich articles between the felt and the conveyor.

If further treatment is desirable, or to shorten the length of theapparatus for given treatment conditions,

further pressure chamber or chambers 41 and nozzles 42 with associatedfan or fans and heaters (not shown) can be provided beneath the pass 35to direct streams or jets of heated gaseous medium upwardly on to thearticles.

By means of the apparatus of the present invention and by applyingsuction to the underneath of the article re ceiving portion of theconveyor, light weight articles which would be prone to being upset ordisplaced when high velocity streams of heated air impinged upon them,can be conveyed through the apparatus and dried therein without becomingsubstantially displaced relatively to the conveyor. This is of advantagewhen such an apparatus is used in combination with moulding apparatusfor producing moulded pulp articles at one end and a receiving orpacking appliance at the other end, as a substantial degree ofregistration between the articles and the conveyor can be maintainedthrough the apparatus, thereby facilitating the design and operation ofthe receiving or packing equipment. Moreover, by using a conveyor with asubstantially flat article-receiving surface such articles can be driedwithout any marked buckling and a measure of flatness can be imparted totheir undersides during drying.

We claim:

1. In a method of thermally treating light-weight moulded pulp articles;the steps of traversing the articles on a perforate conveyor,withdrawing gaseous medium from a suction zone at the side of saidconveyor remote from said articles to establish a pressure drop acrosssaid conveyor, directing a plurality of streams of gaseous mediumtowards articles on the conveyor so as to impinge the articles at highvelocity when opposite said suction zone, withdrawing at the articleside of said conveyor gaseous medium so directed and circulating saidwithdrawn gaseous medium along an endless path of which a portion isoccupied by said high velocity streams, imparting heat to said gaseousmedium before directing it toward said articles, adding gaseous mediumwithdrawn from said suction zone to gaseous medium in said endless path,and adjusting the rate of withdrawal of said gaseous medium from saidsuction zone to be sufficient to restrain said articles fromdisplacement on said conveyor by said high velocity streams.

2. The method set forth in claim 1 wherein said gaseous medium withdrawnfrom said suction zone is mixed with gaseous medium in said endless pathat a point before heat is imparted thereto.

References Cited in the file of this patent UNITED STATES PATENTS1,725,138 Herz Aug. 20, 1929 1,980,558 'Iandel Nov. 13, 1934 2,139,445Dinwiddie Dec. 6, 1938 2,152,167 Ahlmann Mar. 28, 1939 2,235,559 MayerMar. 18, 1941 2,378,703 Hanson June 19, 1945 2,409,298 Merrill Oct. 15,1946 2,558,338 Clements June 26, 1951 2,669,788 Drum et a1. Feb. 23,1954 2,807,892 Gerrish Oct. 1, 1957 2,907,118 M-aescher Oct. 6, 19592,907,120 Black Oct. 6, 1959 2,981,528 Culp Apr. 25, 1961 FOREIGNPATENTS 750,824 Great Britain June 20, 1956

1. IN A METHOD OF THERMALLY TREATING LIGHT-WEIGHT MOULDED PULP ARTICLES;THE STEPS OF TRANSVERSING THE ARTICLES ON A PERFORATE CONVEYOR,WITHDRAWING GASEOUS MEDIUM FROM A SUCTION ZONE AT THE SIDE OF SAIDCONVEYOR REMOTE FROM SAID ARTICLES TO ESTABLISH A PRESSURE DROP ACROSSSAID CONVEYOR, DIRECTING A PLURALITY OF STREAMS OF GASEOUS MEDIUMTOWARDS ARTICLES ON THE CONVEYOR SO AS TO IMPINGE THE ARTICLES AT HIGHVELOCITY WHEN OPPOSITE SAID SUCTION ZONE, WITHDRAWING AT THE ARTICLESIDE OF SAID CONVEYOR GASEOUS MEDIUM SO DIRECTED AND CIRCULATING SAIDWITHDRAWN GASEOUS MEDIUM ALONG AN ENDLWSS PATH OF WHICH A PORTION ISOCCUPIED BY SAID HIGH VELOCITY STREAMS, IMPARTING HEAT TO SAID GASEOUSMEDIUM BEFORE DIRECTING IT TOWARD SAID ARTICLES, ADDING GASEOUS MEDIUMWITHDRAWN FROM SAID SUCTION ZONE TO GASEOUS MEDIUM IN SAID ENDLESS PATH,AND ADJUSTING THE RATE OF WITHDRAWAL OF SAID GASEOUS MEDIUM FROM SAIDSUCTION ZONE TO BE SUFFICIENT TO RESTRAIN SAID ARTICLES FROMDISPLACEMENT ON SAID CONVEYOR BY SAID HIGH VELOCITY STREAMS.